Method of grinding half toroidal CVT disk

ABSTRACT

A half toroidal CVT disk having an inner surface portion, an outer surface portion and a toroidal surface having a given machining allowance is centered with said inner surface portion worked prior to the heat treatment of said half toroidal CVT disk as the standard thereof, and then is chucked by a chuck mechanism. The toroidal surface of the chucked half toroidal CVT disk is ground by a grinding mechanism with the grinding wheel for grinding the half toroidal CVT disk in a state that one of said half toroidal CVT disk and said tool is inclined at a given angle with respect to the other.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of grinding a halftoroidal CVT disk used as a continuously variable transmission in anautomobile.

[0003]2. Description of the Related Art

[0004] A half toroidal CVT disk includes a disk-shaped disk main body 1;and, as shown in FIG. 5, the disk main body 1 has an inner surfaceportion 2 consisting of a through hole formed in the central portionthereof, an outer surface portion 3, and a toroidal surface 4 formed onone surface of the disk main body 1. On one end side of the innersurface portion 2, there is formed an inner surface involute splineportion 5; and, on the other end side thereof, there is formed an insidediameter surface 6. And, the toroidal surface 4, inner surface involutespline portion 5 and inside diameter surface 6, except for the outersurface portion 3, must be respectively ground so as to haveconcentricity accuracy of a given value or higher.

[0005] For this reason, conventionally, for example, as disclosed inJP-A-2000-271844, in a state where the outer surface portion 3 iscentered with the inner surface involute spline portion 5 as thestandard thereof and is chucked in the thus centered state, the outersurface portion 3 is ground; and, with the thus ground outer surfaceportion 3 as the standard thereof, the toroidal surface 4 and innersurface portion 2 are respectively ground in separate steps.

[0006] Also, as a compound grinding machine, conventionally, there isknown a compound grinding machine which, as disclosed in JP-A-10-235545,comprises a plurality of spindle devices each including a work chuck forchucking a work, while these spindle devices are carried on a swingtable which is capable of indexingly swinging in such a manner to beable to correspond to a plurality of operation positions. At theseoperation positions, there are disposed two or more kinds of grindingdevices and, using the grinding devices, the works chucked by the workchucks are respectively ground to thereby shorten the grinding time.

[0007] In case where the toroidal surface and inner surface portion ofthe half toroidal CVT disk are ground in separate steps, it is necessaryto grind the outer surface portion as the common standard surface forsecuring the concentricity of these grinding surfaces. However, to grindthe outer surface portion is not necessary for the function of the halftoroidal CVT disk and thus the step of grinding the outer surfaceportion provides a great factor in the increased cost of the halftoroidal CVT disk.

[0008] Also, there must be secured concentricity between the innersurface involute spline portion to be worked prior to the heat treatmentof the half toroidal CVT disk and the toroidal surface and inner surfaceportion to be ground.

[0009] Further, in case where the outer surface, inner surface portionand toroidal surface are ground sequentially in separate steps, the halftoroidal CVT disk not only must be mounted onto and removed from thegrinding machines but also must be delivered between the grindingmachines in these respective grinding steps, which makes it troublesometo grind the half toroidal CVT disk and thus provides an importantfactor in the increased cost thereof.

[0010] Still further, in the case of the toroidal surface grindingoperation, there is a limit on the diameter of a grinding wheel and thedirection of the rotary shaft of the grinding wheel must be set at anangle of 58°-65° (±15°) with respect to the direction of the rotaryshaft of the work.

SUMMARY OF THE INVENTION

[0011] The present invention aims at eliminating the drawbacks found inthe above-mentioned conventional half toroidal CVT disk grindingmethods. Accordingly, it is a main object of the invention to provide ahalf toroidal CVT disk grinding method which can secure concentricitybetween the inner surface portion and toroidal surface of the halftoroidal CVT disk while omitting the step of grinding the outer surfaceportion thereof, thereby being able to reduce the number ofmanufacturing steps of the half toroidal CVT disk and thus themanufacturing cost thereof.

[0012] Also, it is a second object of the invention to provide a halftoroidal CVT disk grinding method which is capable of not only grindingthe inner surface portion and toroidal surface of the half toroidal CVTdisk simultaneously using a compound grinding machine while they remainchucked by the same chuck mechanism but also securing concentricitybetween the inner surface portion and toroidal surface.

[0013] Further, it is a third object of the invention to provide a halftoroidal CVT disk grinding method which, in case where the inner surfaceportion of the half toroidal CVT disk is hard broached after the halftoroidal CVT disk is thermally treated, can grind the toroidal surfaceof the half toroidal CVT disk with the thus hard broached inner surfaceportion as the standard thereof to omit the step of grinding the outersurface portion the half toroidal CVT disk, thereby being able to reducethe number of manufacturing steps of the half toroidal CVT disk and thusthe manufacturing cost thereof.

[0014] In attaining the above objects, according to a first aspect ofthe invention, there is provided a method of grinding a half toroidalCVT disk by a grinding mechanism with a tool for grinding the halftoroidal CVT disk, the half toroidal CVT disk having an inner surfaceportion, an outer surface portion and a toroidal surface having a givenmachining allowance, the method including the steps of: centering thehalf toroidal CVT disk with a first part of the inner surface portionworked prior to the heat treatment of the half toroidal CVT disk as thestandard thereof; chucking the centered half toroidal CVT disk by achuck mechanism; grinding the toroidal surface of the chucked halftoroidal CVT disk in a state that one of the half toroidal CVT disk andthe tool is inclined at a given angle with respect to the other; andgrinding a second part of the inner surface portion simultaneously withthe toroidal surface in a compound manner.

[0015] Further, according to a second aspect of the invention, there isprovided a method of grinding a half toroidal CVT disk by a grindingmechanism with a tool for grinding the half toroidal CVT disk, the halftoroidal CVT disk having an inner surface portion, an outer surfaceportion and a toroidal surface having a given machining allowance, themethod comprising the steps of: hard-broaching the inner surface portionafter the heat treatment of the half toroidal CVT disk; centering thehalf toroidal CVT disk with the hard broached inner surface portion asthe standard thereof; chucking the centered half toroidal CVT disk by achucking mechanism; and grinding the toroidal surface of the chuckedhalf toroidal CVT disk in a state that one of the half toroidal CVT diskand the tool is inclined at a given angle with respect to the other.

[0016] Now, according to the first aspect of the invention, the halftoroidal CVT disk is centered with the inner surface portion workedprior to the heat treatment of the half toroidal CVT disk as thestandard thereof and is chucked in the thus centered state by the chuckmechanism and, in the centered state, the toroidal surface is ground.Thanks to this, even in case where the step of grinding the outersurface portion of the half toroidal CVT disk is omitted, there can besecured concentricity between the inner surface portion and toroidalsurface of the half toroidal CVT disk. This can decrease the number ofmanufacturing steps of the half toroidal CVT disk, so that themanufacturing cost of the half toroidal CVT disk can be reduced.Further, when the toroidal surface is ground, the inner surface portionis ground simultaneously in a compound manner. This makes it possiblenot only to secure concentricity between the inner surface portion andtoroidal surface of the half toroidal CVT disk but also to shorten thegrinding operation time, thereby being able to reduce the manufacturingcost of the half toroidal CVT disk.

[0017] Further, according to the second aspect of the invention, in casewhere the inner surface portion is hard broached after the heattreatment of the half toroidal CVT disk, in a state where the halftoroidal CVT disk is centered with the thus hard broached inner surfaceportion and is chucked in the thus centered state by the chuckmechanism, the toroidal surface is ground. Due to this, there iseliminated the step of grinding the outer surface portion of the halftoroidal CVT disk to thereby decrease the number of manufacturing stepsof the half toroidal CVT disk, so that the manufacturing cost of thehalf toroidal CVT disk can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic plan view of a grinder, showing a firstembodiment of a method for grinding a half toroidal CVT disk accordingto the invention;

[0019]FIG. 2 is a front view of a chuck mechanism employed in the firstembodiment;

[0020]FIG. 3 is a section view taken along the III-III line shown inFIG. 2;

[0021]FIG. 4 is a longitudinal side section view of a half toroidal CVTdisk including an inner surface ball spline groove, showing a secondembodiment of a method for grinding a half toroidal CVT disk accordingto the invention; and,

[0022]FIG. 5 is a longitudinal side section view of a conventional halftoroidal CVT disk including an ordinary inner surface involute splineportion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Now, description will be given below of the preferred embodimentsof a method for grinding a half toroidal CVT disk according to theinvention with reference to the accompanying drawings.

[0024] FIGS. 1 to 3 show a first embodiment of a method for grinding ahalf toroidal CVT disk according to the invention. As shown in FIG. 1, agrinding machine 10 includes a grinding mechanism 11, a drive mechanism12 and an inner surface grinding unit 13. The grinding mechanism 11includes a cutting table 14, while the cutting table 14 can be driven inthe direction of an arrow mark A shown in FIG. 1 through a ball screw 15by a servo motor 16.

[0025] The cutting table 14 includes a drive motor (not shown) which candrive and rotate a grinding wheel 17, that is, the rotational force ofthis drive motor can be transmitted to the grinding wheel 17 through aspindle 18. The grinding surface of the outer peripheral surface of thegrinding wheel 17 is formed in a curved shape having a radiuscorresponding to the toroidal surface 19 a of a half toroidal CVT disk(which is hereinafter referred to as a work 19) which is a finishedproduct with the grinding operation thereof completed. Therefore, sincethe work 19 has a machining allowance in a state before it is ground,the radius of the surface to be ground of the work 19 is set smallerthan the diameter of the grinding surface of the outer peripheralsurface of the grinding wheel 17. Here, an angle a between the rotationcenter axis a of the work 19 and the center axis b of the grinding wheelis set in the range of 58°-65° (±15°).

[0026] The drive mechanism 12 includes a drive motor (not shown), whilethis drive motor includes a chuck mechanism 20 for chucking the work 19.The chuck mechanism 20 is structured as shown in FIGS. 2 and 3. That is,a chuck main body 21 includes a work receiving portion 22 formed in thefront portion thereof and, in the central portion of the work receivingportion 22, there is disposed a collet 24 which is connected to a drawbar 23.

[0027] And, in case where the work 19 is set on the work receivingportion 22, the collet 24 is inserted into the inner surface involutespline portion 19 b of the work 19. In this state, in case where thedraw bar 23 is pulled in the direction of an arrow mark B shown in FIG.3, the collet 24 is allowed to spread, thereby being able to hold theinner surface involute spline portion 19 b of the work 19. At the thentime, the work 19 is also pulled in the same direction and is therebybutted against the standard surface of the work receiving portion 22.

[0028] Further, on the outer periphery of the work receiving portion 22of the chuck main body 21, there is disposed a floating chuck mechanism25. The floating chuck mechanism 25 includes three pawls 26 so that theouter periphery of the work 19 can be held at three positions spaced atregular intervals of 120° by these three pawls 26, while the three pawls26 are respectively connected to their associated cylinders 29 throughtheir associated levers 28 which can be rotated about their associatedpivots 27.

[0029] And, in case where the levers 28 are pulled by the cylinders 29respectively, the levers 28 can be respectively rotated about theirpivots 27 and the pawls 26 can be respectively moved toward the work 19,thereby holding the outer surface portion 19 c of the work 19. At thethen time, even in case where the inner surface portion 19 d and outersurface portion 19 c of the work 19 happen to be out of concentricitywith each other, due to the action of the floating chuck mechanism 25,there is eliminated the possibility that the pawls 26 can be made freeor can be strongly pressed against the outer surface portion 19 c of thework 19 in part.

[0030] Now, the inner surface grinding unit 13, as shown in FIG. 1,includes an inner surface grinding cutting table 31 and an inner surfacegrinding traverse table 32 which is carried on the inner surfacegrinding cutting table 31. The inner surface grinding cutting table 31can be driven in the direction of an arrow mark c shown in FIG. 1through a ball screw 33 by a servo motor 34, while the inner surfacegrinding traverse table 32 can be driven in the direction of an arrowmark d shown in FIG. 1 through a ball screw 35 by a servo motor 36.

[0031] The inner surface grinding traverse table 32 carries an innersurface grinding spindle 37 thereon and, on the inner surface grindingspindle 37, there is mounted an inner surface grinding wheel 30. And,the inner surface grinding wheel 30 is used to grind the inner surfaceportion 19 d of the work 19.

[0032] Next, description will be given below of the operation of theabove-described first embodiment of a half toroidal CVT disk accordingto the invention.

[0033] That is, the work 19 chucked by the chuck mechanism 20 is rotatedusing the drive motor (not shown) of the drive mechanism 12 and, at thesame time, the grinding wheel 17 of the grinding mechanism 11 is rotatedusing the drive motor (not shown). In this state, in case where thecutting table 14 is moved in the A direction using the servo motor 16,the grinding wheel 17 moves forward in the radial direction C shown inFIG. 3 with respect to the toroidal surface 19 a of the work 19 and thuscuts the toroidal surface 19 a to thereby grind the same.

[0034] On the other hand, at the then time, since not only the innersurface grinding wheel 30 mounted on the inner surface grinding spindle37 is rotated but also the inner surface grinding cutting table 31 ismoved in the arrow mark c direction by the servo motor 34 to execute acutting operation, the inner surface portion 19 d of the work 19 isground simultaneously by the inner surface grinding wheel 30, that is,the inner surface portion 19 d is ground in a compound manner.

[0035] In this manner, in a state where the toroidal surface 19 a iscentered with the inner surface involute spline portion 19 b workedprior to execution of the heat treatment of the half toroidal CVT diskserving as the work 19 as the standard thereof and is chucked by thechuck mechanism 20, the toroidal surface 19 a is ground. Thanks to this,even in case where the step of grinding the outer surface portion 19 cis omitted, concentricity between the inner surface portion 19 d andtoroidal surface 19 a can be secured. This can reduce the number of themanufacturing steps of the half toroidal CVT disk, which in turn makesit possible to reduce the manufacturing cost thereof.

[0036] By the way, in the case of a light grinding operation, only thecollet chucking function of the chuck mechanism 20 can providesufficient holding rigidity for the work 19. However, in the case of agrinding operation to be executed in the present embodiment, thetoroidal surface 19 a must be ground in a wide range and, in some cases,the grinding resistance in the radial direction can range up to 40 kgf.In such case, there is a possibility that the work 19 can be moved orshifted in position, which lowers the grinding accuracy (roundness andchatter). Therefore, in order to obtain more sufficient holdingrigidity, the outer surface portion 19 c of the work 19 is held by thefloating chuck mechanism 25. However, it should be noted here that thefloating chuck mechanism 25 is not always necessary.

[0037] Also, in the above-mentioned first embodiment, when the toroidalsurface 19 a is ground in a state where it is centered with a part ofthe inner surface involute spline portion 19 b of the half toroidal CVTdisk serving as the work 19 as the standard thereof and is chucked bythe chuck mechanism 20, the inner surface portion 19 d is groundsimultaneously with the grinding of the toroidal surface 19 a, that is,in a compound manner by the inner surface grinding wheel 30. Thanks tothis, concentricity between the inner surface portion 19 d and toroidalsurface 19 a can be secured as well as the grinding operation time canbe shortened, thereby being able to reduce the manufacturing cost of thehalf toroidal CVT disk.

[0038] Now, FIG. 4 shows a second embodiment of a method for grinding ahalf toroidal CVT disk according to the invention. In the secondembodiment, in the inner surface portion of a work 19 which consists ofa different half toroidal CVT disk from the disk 19 employed in thefirst embodiment, there is formed an inner surface ball spline groove 19e. In the case of the work 19 having such inner surface ball splinegroove 19 e, after it is thermally treated, the inner surface ballspline groove 19 e must also be worked.

[0039] For example, the inner surface ball spline groove 19 e and innersurface portion 19 d can be worked integrally by hard broaching. In thiscase, in a state where the thus hard broached inner surface portion 19 dis chucked by the chuck mechanism 20 according to the first embodimentand the concentricity of the toroidal surface 19 a with the hardbroached inner surface portion 19 d is secured, the toroidal surface 19a is ground using the grinding wheel 17.

[0040] In case where only the inner surface ball spline groove 19 e ishard broached but the inner surface portion 19 d is not hard broachedafter the disk 19 is thermally treated, after the inner surface ballspline groove 19 e is received by its associated ball and is thencentered, in order to secure the rigidity and holding force of the disk19, the outer surface portion 19 c is chucked by a floating chuckmechanism 25 similar to that of the first embodiment and the toroidalsurface 19 a is then ground.

[0041] In this manner, in case where the inner surface portion of thework is hard broached after the work is thermally treated, the toroidalsurface of the work is ground with the thus hard broached inner surfaceas the standard thereof. This eliminates the need to grind the outersurface portion of the work, thereby being able to reduce the number ofmanufacturing steps of the half toroidal CVT disk. As a result of this,the manufacturing cost of the half toroidal CVT disk can be reduced.

[0042] While only certain embodiments of the invention have beenspecifically described herein, it will apparent that numerousmodifications may be mede thereto without departing from the spirit andscope of the invention.

[0043] As has been described heretofore, according to the first aspectof the invention, even in case where the step of grinding the outersurface of a half toroidal CVT disk is omitted, concentricity betweenthe inner surface portion and toroidal surface of the half toroidal CVTdisk can be secured. This can decrease the number of manufacturing stepsof the half toroidal CVT disk, so that the manufacturing cost of thehalf toroidal CVT disk can be reduced. Further, the inner surfaceportion and toroidal surface of the half toroidal CVT disk can be groundsimultaneously in a compound manner by a compound grinding machine whilethey remain chucked simultaneously by the same chucking mechanism. Thismakes it possible not only to secure concentricity between the innersurface portion and toroidal surface of the half toroidal CVT disk butalso to shorten the grinding operation time, thereby being able toenhance the productivity of the half toroidal CVT disk.

[0044] According to the second aspect of the invention, in case wherethe inner surface portion of the half toroidal CVT disk is hard broachedafter the disk is thermally treated, the toroidal surface of the halftoroidal CVT disk can be ground with the thus hard broached innersurface portion as the standard thereof. This eliminates the step ofgrinding the outer surface of the half toroidal CVT disk and thusdecreases the number of manufacturing steps of the half toroidal CVTdisk, thereby being able to reduce the manufacturing cost of the halftoroidal CVT disk.

What is claimed is:
 1. A method of grinding a half toroidal CVT disk bya grinding mechanism with a tool for grinding said half toroidal CVTdisk, the half toroidal CVT disk having an inner surface portion, anouter surface portion and a toroidal surface having a given machiningallowance, said method comprising the steps of: centering said halftoroidal CVT disk with a first part of said inner surface portion workedprior to the heat treatment of said half toroidal CVT disk as thestandard thereof; chucking said centered half toroidal CVT disk by achuck mechanism; grinding said toroidal surface of said chucked halftoroidal CVT disk in a state that one of said half toroidal CVT disk andsaid tool is inclined at a given angle with respect to the other; andgrinding a second part of said inner surface portion simultaneously withsaid toroidal surface in a compound manner.
 2. A method of grinding ahalf toroidal CVT disk by a grinding mechanism with a tool for grindingsaid half toroidal CVT disk, said half toroidal CVT disk having an innersurface portion, an outer surface portion and a toroidal surface havinga given machining allowance, said method comprising the steps of:hard-broaching said inner surface portion after the heat treatment ofsaid half toroidal CVT disk; centering said half toroidal CVT disk withsaid hard broached inner surface portion as the standard thereof;chucking said centered half toroidal CVT disk by a chuck mechanism; andgrinding said toroidal surface of said chucked half toroidal CVT disk ina state that one of said half toroidal CVT disk and said tool isinclined at a given angle with respect to the other.
 3. A half toroidalCVT disk manufactured by the method of claim 1, wherein said outersurface portion is free from grinding after the heat treatment.
 4. Ahalf toroidal CVT disk manufactured by the method of claim 2, whereinsaid outer surface portion is free from grinding after the heattreatment.
 5. A half toroidal CVT disk, comprising: an inner surfaceportion adapted to be inserted with an input shaft of a half toroidalCVT therein; an outer surface portion; and a toroidal surface with acurved shape adapted to be brought into contact with a power roller ofsaid half toroidal CVT, wherein said outer surface portion is free fromgrinding after the heat treatment.